An ink jet printer of the so-called "drop-on-demand" type has at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink may be contained in a plurality of channels where power pulses are used to cause the droplets of ink to be expelled, as required, from orifices or nozzles at the ends of the channels.
In a thermal ink jet printer, the power pulses that result in a rapidly expanding gas bubble to eject the ink from the nozzle are usually produced by resistors, each located in a respective one of the channels, which are individually addressable by voltage pulses to heat and vaporize ink in the channels. As voltage is applied across a selected resistor, a vapor bubble grows in that particular channel and ink bulges from the channel orifice. At that stage, the bubble begins to collapse The ink within the channel retracts and separates from the bulging ink which forms a droplet moving in a direction away from the channel orifice and towards the recording medium. The channel is then re-filled by capillary action, which in turn draws ink from a supply container. Operation of a thermal ink jet printer is described in, for example, U.S. Pat. No. 4,849,774.
One particular form of thermal ink jet printer is described in U.S. Pat. No. 4,638,337. That printer is of the carriage type and has a plurality of printheads, each with its own ink supply cartridge, mounted on a reciprocating carriage. The nozzles in each printhead are aligned perpendicularly to the line of movement of the carriage and a swath of information is printed on the stationary recording medium as the carriage is moved in one direction. The recording medium is then stepped, perpendicularly to the line of carriage movement, by a distance equal to the width of the printed swath. The carriage is then moved in the reverse direction to print another swath of information.
A pagewidth ink jet printer is described in U.S. Pat. No. 5,192,959. The pagewidth printer includes a full width printhead or printbar which is stationary during printing operations. A sheet of paper is stepped past the printhead and ink is ejected along the entire width of the recording medium for recording images.
It has been recognized that there is a need to maintain the ink ejecting nozzles of an ink jet printhead, for example, by periodically cleaning the orifices when the printhead is in use, and/or by capping the printhead when the printer is out of use or is idle for extended periods. The capping of the printhead is intended to prevent the ink in the printhead from drying out. There is also a need to prime a printhead before use, to ensure that the printhead channels are completely filled with ink and contain no contaminants or air bubbles and also periodically to maintain proper functioning of the nozzles. Maintenance and/or priming stations for the printheads of various types of ink jet printer are described in, for example, U.S. Pat. Nos. 4,855,764; 4,853,717 and 4,746,938 while the removal of gas from the ink reservoir of a printhead during printing is described in U.S. Pat. No. 4,679,059.
It has been found that before the printing operation begins it is necessary to draw ink through the printhead nozzles to thereby fill the channels and nozzles with ink so that printing can begin with accurate placement of the ejected ink upon the medium It has also been found that under certain conditions the ink channels or nozzles will become clogged with debris or with dried ink. In such situations, the printhead must be primed to remove the unwanted material by vacuum priming. In vacuum priming, a priming element is placed against the face of a printhead to cover the nozzles. A vacuum is applied to the nozzles through the priming element and ink is drawn from the printhead, through the priming element, and to a waste container. The priming element is typically made of a flexible and resilient material such as rubber which can collapse under pressure of the applied vacuum.
In U.S. Pat. No. 4,567,494 to Taylor, a nozzle cleaning and priming apparatus for ink jet printers is described. A hollow cylindrical suction cup includes a drain pipe for connection to a suction tube. A second cup made of foam is positioned within the hollow of the cup. The suction tube pulls ink from the printhead and through the foam cup under the application of a vacuum.
U.S. Pat. No. 5,250,962 to Fisher et al. describes a movable priming station for use with an ink jet printer. The movable priming station includes a vacuum port. The vacuum port can be provided with a suction tip which can be oval shaped.
U.S. Pat. No. 5,117,244 to Yu describes a nozzle capping device to cap a thermal ink jet printhead without moving the printhead or a paper transport. A resilient gasket which contains magnetic material is attached to the printhead by a relatively thin flexible boot or sleeve. A steel bar is disposed beneath the paper transport belt. The resilient gasket is either attracted to the steel bar for capping the printhead or attracted to the printhead by an electromagnet for printing operations.
U.S. patent application Ser. No. 08/200,605, filed Mar. 30, 1994, entitled "Ink Jet Printer Priming Element," to Hermanson describes a priming element for priming or maintaining the ink ejecting orifices of an ink jet printhead. The priming element contacts the face of an ink jet printhead and includes support members which prevent the priming element from collapsing during priming/maintenance operations.
U.S. patent application Ser. No. 08/084,095 filed Jul. 1, 1993, entitled "Ink Jet Maintenance Subsystem" to Anderson et al. describes an ink jet maintenance station and an articulating cap assembly to facilitate capping of ink jet printbar nozzles.